1. Field of the Invention
The present invention relates to a method for smoothly evaginating a tubular material wherein a flexible tubular material is evaginated by drawing a rope passed through the tubular material from the outside while applying a fluid pressure to the portion of the tubular material placed in a pressure container to push out the tubular material from the container by inner fluid pressure. More particularly, the present invention relates to a method for smoothly evaginating a tubular lining material within pipe lines such as those made of steel or the like metal, concrete pipes or rigid resinous pipes, chiefly those already constructed and subjected to actual use, for example, underground pipelines such as gas conduits, city water pipes and pipes enclosing power transmission wires or telephone cables, and simultaneously bonding the evaginated lining material onto the inner surface of the pipe lines thereby reinforcing the pipe lines or repairing damaged portions thereof, wherein a tubular lining material is evaginated and at the same time bonded to the inner surface of the pipe lines by previously applying a binder onto the inner surface of the lining material, previously passing a rope through the lining material beyond its full length, and drawing the rope from the outside while applying a fluid pressure to the portion of the lining material placed in a pressure container to push forward the lining material within the pipe lines while undergoing evagination through a discharge pipe of the container by inner fluid pressure.
2. Description of the Prior Art
It is well known that a hose such as a fire hose with a lining of a rubber or a synthetic resin is manufacture by coating the external surface of a textile jacket made of woven or knitted fibers in a tubular form with a film of such rubber or resin and then evaginating the jacket. The methods disclosed in British Pat. No. 957,929 and U.S. Pat. No. 3,927,184 are involved in such practice, among which the latter method is most advantageous in that the operation is easy and simple. This method comprises fixing one end of an externally coated hose placed in a pressure container to an annular fastener of a nozzle and applying a fluid pressure to the container to effect evagination of the hose by inner pressure. When the hose is extremely long, however, a very high pressure is required to initiate evagination whereby fluctuation in evagination velocity occurs during the treatment, thus forming torsion in the resultant hose. In the extreme case, the hose is not evaginated and is damaged by the extremely high pressure.
On the other hand, it is known that superannuation or damage of underground pipe lines for gas or water often causes dangerous leakage of gas or water. Further, deteriorated pipes or casings enclosing power transmission wires or telephone cables permit intrusion of water or electroconductive substances and result in accidents caused by electric leakage. A sole effective coountermeasure from the past to prevent such troubles is that when such underground pipe lines are superannuated, the pipe lines are dug up over the length in the order of several ten or hundred meters and replaced with new ones. In this case, however, supply of city water or gas has to be discontinued until the pipe-exchange work has been finished. In case superannuated pipes are buried under public roads, people encounter a great deal of trouble and inconvenience since traffic on the roads is limited during the pipe-exchange work. It is a matter of course that much labor and cost are required for exchange of pipes in addition to the difficulty in the work itself. Furthermore, it is not rare that such pipe-exchange work cannot be utilized, depending on the particular situation of the place where such pipe lines are buried. Recently, the strong probability of severe earthquakes are geophysically predicted in many places in the world and consideration is being given to reinforcing underground pipes regardless of whether such pipes are superannuated or not to protect them from damage by earthquake. However, such pipe-exchange work on the underground pipe lines over the almost full length thereof is extremely difficult or rather impossible for both technical and economical reasons and is utterly ineffective for the purpose of reinforcing the pipe lines.
Under such circumstances, a primitive pipe-lining method wherein a flexible plastic tube is inserted into underground pipe lines and bonded to the inner surface thereof was proposed for attaining both purposes of reparing damaged portions of the pipe lines and reinforcing them so as to withstand mechanical shock. In such a method, however, the step for inserting the flexible tube into the underground pipe lines is extremely difficult so that the work is almost impossible to operate in such place where the pipes are long and/or curved. With a view to improving this primitive method, a new method for providing pipe lines with a lining material with evagination wherein a flexible tube is inserted into a pipe while turning the tube inside out by the action of a pressurized fluid, such as compressed air, and bonded at the same time onto the inner surface of the pipe by the aid of a binder, was developed and has been watched with interest in recent years. A method of this type is desclosed in U.S. Pat. Nos. 2,794,785, 3,132,062, 3,230,129 and 3,494,813 and British Pat. Nos. 1,002,131, 1,069,623 and 1,025,011 and is certainly advantageous in that insertion of the lining material and bonding of the material to the inner surface of the pipe are effected smoothly, at the same time.
Among these prior art approaches, British Pat. No. 1,002,131 relates to a method and device for evaginating a flexible tube but nowhere gives any description or suggestion on insertion of the tube into a pipe. British Pat. No. 1,025,011 discloses the means for inserting a tube into a pipe while turning the tube inside out. In this patent, however, the tube is not bonded to the inner surface of the pipe and no technique is disclosed for this purpose. U.S. Pat. Nos. 2,794,758, 3,132,062 and 3,494,813 and British Pat. No. 1,069,623 disclose respectively a method for inserting a tube into a pipe while turning the tube inside out and bonding the tube onto the inner surface of the pipe. However, all of these known approaches disclosed in these patents require the previous application of a binder onto the inner surface of a pipe or tube prior to insertion of the tube. Further, an ordinary binder containing a volatile component cannot be used for this purpose because both pipe and tube should be impervious. Accordingly, the use of a binder of the type that contains no volatile component and wherein the resinous component is curable only after the lapse of a long period of time comes into question in these methods. As a considerably longer period of time is required until such binder has completely been applied onto the inner surface of the pipe, curing of the binder already starts prior to the insertion of the tube into the pipe, thus resulting in insufficient adhesion of the lining material. The use of a binder having an extended pot life is thus required to prevent such premature curing and the time necessary for the lining treatment thus becomes inevitably long. U.S. Pat. No. 3,230,129 disclosed a method wherein the inside of a pipe is charged with a binder and a tube is inserted into the pipe from one end thereof while turning the tube inside out and pushing the binder forward thereby bonding the evaginated portion of the tube onto the inner surface of the pipe by the aid of the binder remaining on the inner surface. However, this method has also a number of drawbacks. First, the quantity and distribution of the binder cannot be controlled so that the binder is applied unevenly onto the inner surface of the pipe. Secondly, the binder must be used in an amount larger than that needed for bonding the tube to the pipe because the tube is allowed to proceed with simultaneous evagination within the pipe while pushing the binder forward. An excess amount of the binder is, after all, discarded. Thirdly, when the pipe is inclined, the head pressure of the binder acts on the top or turning point of the proceeding tube where evagination occurs, so that the pressure required for evagination of the tube fluctuates and the amount of the binder applied tends to vary. Thus, none of the prior art methods succeeded in providing pipes, especially those buried in the ground, with a lining material according to a simple operation conducted in situ without moving or disjoining the pipes.
In the above circumstances, the present inventors already have proposed with co-workers a new improved method for providing the inner surface of pipes with a tubular lining material (Japanese Laid-open Patent Appln. No. 55-91627) wherein the tubular lining material is inserted into the pipes while turning it inside out and applying at the same time a binder onto the inner surface of the lining material evenly and the lining material is bonded onto the inner surface of the pipes with the binder being interposed therebetween under pressure of a pumped fluid. According to this improved method, a number of disadvantages of the prior art methods could entirely be overcome by a series of specific treatments wherein a reservoir of a binder is formed in the interior of the unevaginated portion of a tubular lining material positioned in the rear of the fixed point of the lining material to a pipe and a fluid pressure is applied externally to the portion of the lining material where the reservoir is formed, thereby pushing the lining material forward under evagination within the pipe and squeezing the lining material at the same time to adjust the quantity of the binder applied onto the inner surface of the lining material. In a preferred embodiment shown in FIG. 6 of this improved method wherein an induction pipe is inserted between a pipe in the ground and a discharge pipe in front of the pressure container, the lining treatment for pipes in the ground is markedly facilitated since the size of a hole to be dug for accommodating the pressure evagination device and workers for handling it can be minimized and most of the apparatus can be left on the ground. Thus, this improved method is fundamentally an excellent method for applying a lining material onto the inner surface of a pipe line having a length in the order of several hundred meters and/or a number of curved portions. Because of easiness in operations for achieving a high efficiency of lining treatments, this improved method is indeed advantageous in providing the inner surface of a pipe line in the ground with a reinforcing lining material and is now being watched with high interest.
According to the present inventors' further study, however, it was found that when a pipe line to be lined is as long as one thousand meters or more or when the pipe line has a number of curved portions such as bends, elbows and/or offset bends, the fluid pressure required for evagination of a lining material should be high enough, especially in the final stage of the treatment, so that this method encounters a number of unexpected difficulties. For example, the pressure container for effecting evagination of the lining material under pressure should be made of a material resistant to high pressure to prevent danger of any bursting of the pressure container. When the evagination of a lining material is effected under high pressure, there is a fear of breakage of the lining material at the turning point where evagination takes place. Under high pressure, the lining material is bonded, while receiving strain corresponding to such high pressure, to the inner surface of the pipe, especially in curved portions. When the high pressure is reduced after completion of the lining treatment, a force eliminating such strain is acted on the curved portions where the bonded lining material is partially detached from the inner surface. In general, the lining material can be evaginated and at the same time bonded to the inner surface of the pipe under a relatively low fluid pressure at the initial stage of the lining treatment. At the middle and final stages of the treatment, however, a relatively high fluid pressure is required for evagination and bonding of the lining material. Such high fluid pressure is also required temporarily when the lining material is passed through curved portions of the pipe line. During the lining treatment, therefore, a considerable fluctuation of pressure is unavoidable which apparently results in reduction of the bonding force of the lining material due to its elongation or shrinkage caused by the fluctuation of pressure. Further, fluctuation of pressure causes fluctuation in the amount of a binder applied onto the inner surface of the lining material so that even bonding force of the lining material is not achieved. Even by the use of the improved method, the operation under high pressure causes a number of drawbacks, especially in the treatment of a pipe line having a very extended length and/or many curved portions. In the practical aspect, therefore, there is a great demand for making further improvement in the above method so that the operation may be conducted under a relatively low pressure even in the treatment of a pipe line having an extended length or abounding in curved portions.